Fix some nits in release flow

[Leko]

• echo -> cat
• reference lerna.json instead of package.json

[codecov-io]

Codecov Report

Merging #13 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #13   +/-   ##
=======================================
  Coverage   26.73%   26.73%           
=======================================
  Files           5        5           
  Lines         101      101           
  Branches       18       18           
=======================================
  Hits           27       27           
  Misses         63       63           
  Partials       11       11

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